Avalanche breakdown and breakdown luminescence of AlGaN multiquantum wells

AlGaN $p-i-n$ diodes were fabricated on 6H-SiC substrate using $Al0.1Ga0.9N∕Al0.15Ga0.85N$ multiquantum wells (MQWs) for the active region. Avalanche breakdown and breakdown luminescence of these AlGaN MQW diodes were experimentally investigated. Breakdown electroluminescence from the MQW active layers was observed for unusually low bias values of 9 V. A continuous red shift of the interband luminescence resulting from the Stark effect was observed with increasing reverse bias. The breakdown threshold was found to be as low as 9 V. Polarization-induced electric fields in the $Al0.1Ga0.9N$ well layers were found to have the same direction as the applied field. These polarization fields greatly enhance the ionization coefficient of electrons and help lower the threshold for avalanche breakdown. Substantial enhancement of the ionization coefficient produced by the polarization fields is quantitatively demonstrated with $GaN∕AlGaN$ quantum wells by considering a polarization field with the same direction as the applied field within the GaN well layers.